The present invention relates generally to fabrication systems, and more particularly to fabrication systems for manufacturing substrates within environmentally controlled fabrication tools.
In the semiconductor integrated circuit fabrication industry, a single defect can destroy an entire wafer die by disrupting features essential to the semiconductor devices formed therein. Defects also can degrade device performance and reliability by creating leakage paths, generating undesirable localized fields, and the like.
A defect can arise when a particle lands on a wafer. Particles commonly arise from humans, the environment in which the wafer is processed (e.g., particles generated by friction between moving objects within the processing chamber), as well as from films deposited or grown on the wafer.
To reduce particle-induced defects, wafers are fabricated in a clean environment, and are mass produced in a large enclosed clean area known as a FAB, which contains a plurality of processing tools that are often roughly arranged along a grid to make transport efficient. A grid layout facilitates wafer transport organization, and enables automated wafer transport. Currently, within a grid layout processing chambers and tools which supply wafers thereto are treated as a production unit and FAB control software treats each such production unit as an independent entity.
Two primary grid layouts are 1) a bay and chase layout, and 2) a ballroom layout, each of which is shown in FIGS. 1A and 1B respectively.
FIG. 1A shows a bay and chase layout 11a comprising a clean transport aisle 13 which branches into a plurality of branch transport aisles 15. A clean room wall 17 defines the clean transport aisle 13 and the branch transport aisles 15. When defined by a clean room wall 17 the branch transport aisles are known as bays.
Behind the wall is an area known as a chase 19 which contains a plurality of processing tools 21. Each of the processing tools 21 has a load port positioned adjacent an opening in the clean room wall 17 so that wafer carriers may be transported along the clean transport aisle 13, into a bay 15, and through the clean room wall 17 into a processing tool 21.
FIG. 1B shows a ballroom layout 11b. The ballroom layout 11b is identical to the bay and chase layout 11a of FIG. 1 except the clean room wall 17 is omitted. In this case, more of the support facilities are on the floor underneath the processing tools 21.
In either the layout of FIGS. 1A or 1B, the processing tools 21 may comprise an environmentally sealed semiconductor device fabrication tool (hereinafter a xe2x80x9cfabrication toolxe2x80x9d). A fabrication tool typically includes at least one load port which receives a wafer carrier housing one or more wafers and which places the wafer carrier into the tool""s environment; at least one processing chamber for performing processing on wafers extracted from the wafer carrier, and possibly one transfer chamber containing a wafer handler adapted to transfer wafers between the load lock and the processing chamber.
Further, in either the layout of FIGS. 1A or 1B, the FAB 11a, 11b can be maintained as a clean room, having filters and/or other mechanisms for removing particles from the environment. Such a clean room is monitored to ensure that the level of particles per cubic foot of clean room does not exceed a predetermined level or clean room xe2x80x9cclassxe2x80x9d. However, due to the amount of filtering required, it is extremely expensive to achieve the highly clean environment required of an area in which a wafer or wafer carrier is exposed to the environment outside the fabrication tool. Typically a class 1 environment having fewer than about 7,000particles of 0.5 micron size or larger per cubic foot is required of such areas. Thus many FABs use sealed wafer carriers that enclose the wafers in a clean, mini-environment during transport allowing the cleanliness level of the FAB as a whole to be reduced.
Generally, within a bay and chase layout 11a, because a fabrication tool maintains wafers and wafer carriers in a controlled environment after they are loaded into the load lock and the desired environment is achieved, the clean room wall 17 divides the clean room into two areas, a white area having a high cleanliness level as wafers may be exposed to the environment while in those areas (e.g., in the bay 15 and/or the clean transport aisle 13) and a gray area having a lower cleanliness level than the white area as wafers may be sealed within a wafer carrier or within a fabrication tool 21 while in those areas (e.g., the chase 19). Because wafers and/or wafer carriers are exposed to the environment adjacent the load lock, the load lock of a fabrication tool is positioned with a sealable opening thereof (e.g., a slit valve or a door) extending through the clean room wall 17 such that the area adjacent the load lock""s opening is maintained as a white environment. The remainder of the fabrication tool 21 is maintained within the gray environment of the chase 19, typically a class 100 environment having fewer than about 700,000 particles of 0.5 micron size or larger per cubic foot.
The bay and chase layout (FIG. 1A) is intended to reduce clean room costs by allowing for a gray area where less filtering is required. However, the clean room wall 17 and the differing clean room gowning (e.g., special clothing) requirements between the gray area and the white area hinders access to the fabrication tool. In contrast, the ballroom layout (FIG. 1B) allows free access to the area surrounding the fabrication tool. A ballroom FAB is maintained at a less expensive cleanliness level, intermediate the white and gray areas. However, wafers must be transported in sealed carriers or xe2x80x9cpodsxe2x80x9d. In both the ballroom and the bay and chase layouts, the addition of processing tools 21 requires elongation of the branch transport aisle 15 (or the addition of more aisles) and increases the complexity of managing the FAB due to the dispersal of like equipment and due to the increased complexity of the software program that controls wafer transport within the FAB 11a, 11b (because, as described further below, additional tool loading platform locations must be included in the program). Regardless of the layout employed, construction of a FAB remains costly due to both clean room costs and the significant capital investment required to provide a fault tolerant system (i.e., a system having a sufficient number of tools to maintain a desired production rate (wafers/hour), despite the inevitable tool downtime required for tool repair and maintenance ).
Accordingly, there is a need for a fabrication system design that facilitates a gradual or staged increase in fabrication tool numbers, and that minimizes the white area of the clean room. Further, improved business methods are required to reduce initial equipment costs while maintaining a fault tolerant FAB.
The present invention provides a FAB configuration which locally organizes production units or processing tools such that production capacity can be independently adjusted for each process step. Accordingly, process capacity can be added without requiring branch transport aisle elongation, and without requiring the programming of additional tool load ports into the program that controls the FAB. The inventive FAB configuration, referred to herein as a SuperFrame, arranges tools in sets. Each tool in a tool set is coupled to the branch transport aisle via a common storage-movement apparatus which is positioned perpendicular to the branch transport aisle. The common storage-movement apparatus has one or more factory load ports adapted to receive wafer carriers from the branch transport aisle. Similarly, the tool set and the storage-movement apparatus has one local control program that supervises the tool set and the storage-movement apparatus and presents the tool set and the storage-movement apparatus to the FAB as one unit.
Additionally a method of reducing capital equipment costs without reducing fault tolerance is provided. Specifically, an additional processing tool, not needed for steady state processing, is provided in exchange for periodic (e.g., monthly or quarterly) payment. Alternatively, payment may be conditioned on future use. Thus, a manufacturer has an additional tool which provides backup capability or fault tolerance, yet does not have the initial capital investment cost of purchasing the additional tool.